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LIVE LOADS <br />The AASHTO design loads commonly used in the <br />past were the HS 20 with a 32,000 pound axle load in <br />the Normal Truck Configuration, and a 24,000 pound axle <br />load in the Alternate Load Configuration(Figure 2). <br />The AASHTO LRFD design loads are the HS 20 with <br />a 32,000 pound axle load In the Normal Truck <br />Configuration, and a 25,000 pound axle load in the <br />Alternate Load Configuraticn(Figure 2). In addition, the <br />AASHTO LRFD requires the application of a 640 pound <br />per linear foot Lane Load applied across a 10 foot wide <br />C lane at all depths of earth cover over the top of the pipe, <br />` up to a depth of 8 feet. This Lane Load converts to an <br />additional live load of 64 pounds persquare foot, applied <br />l to the top of the pipe for any depth of burial less than 8 <br />feet. The average pressure intensity caused by a wheel <br />load is calculated by Equation 2. The Lane Load intensity <br />is added to the wheel load pressure intensity in Equation <br />3. <br />The HS 20, 32,000 pound and the Alternate Truck <br />25,000 pound design axle are carried on dual <br />wheels(Figure 1). The contact area of the dual wheels <br />with the ground Is assumed to be a rectangle(Figure 1), <br />with dimensions presented in Table 1. <br />16000 lb. HS 20 Load <br />12500 lb. LRFD Alternate Load <br />0.83 <br />(10In.) b <br />a <br />I, 1.67 ft. 1 <br />(20 in.) <br />a(width), ft(In.) b(length), ft(In.) <br />1.67(20) 0.63(10) <br />IMPACTFACTORS <br />The AASHTO LRFD Standard applies a dynamic <br />load allowance to account for the truck load being non- <br />static.The dynamic load allowance, IM, is determined by <br />Equation 1: <br />IM= 33(1.0-0.125H) <br />100 <br />(1) <br />where: H = height of earth cover over the top of the <br />pipe, ft. <br />HS 20 Load HS 20 Load <br />4000 lb. 4000 I b. 4000 lb. 4000 lb. <br />00- <br />16000 lb. <br />O j O 0 <br />I <br />6 ft, -- 14 ft. — 6 ft. 14 ft. <br />-o0 00 00 <br />1 <br />16000 lb. 16000 I b. 16000 lb. <br />LRFD Alternate Load <br />14 ft. 12500lb. 12500lb. <br />to <br />30ft. OO OO <br />-001 00 00 41" <br />16000 lb. 12500lb. 12500lb. <br />HS 20 & LRFD Alternate Loads <br />4 fL <br />2 1 American Concrete Pipe Assoclatlon • 222 W. Las C011 1 • Irving, TX 75039 • (972) 506.7216 • FAX (972) 506.7682 <br />a a , <br />